Do Battery-Pack Failures Reduce the Life of Hybrid Cars? A Reader Asks

I have a 1997 Saturn that, remarkably, is still running. It probably has the book value of a large watermelon, so if anything major goes wrong with it, that’s the end of that.

If that Saturn were a hybrid, I’m guessing the battery pack would have died about four years ago, give or take. But replacing a battery pack would be a huge expense, no? And the older the car gets, the less incentive there is to incur this huge expense.

So it seems to me that hybrids have a significant built-in obsolescence factor–while at the same time their higher up-front cost means you need to hold on to them longer to recoup the cost.

What, then, is the logic behind buying a hybrid…or an electric, for that matter…over an efficient gasoline or diesel vehicle?

The broader universe of car buyers who say they want a green car really want to save money. So they may or may not buy a hybrid, since retail buyers routinely overweight the importance of purchase price and ignore the impact of total cost of ownership (maintenance, repairs, gasoline cost) over the lifetime of the car.

Whether a hybrid really save you money depends on your duty cycle: whether you spend a lot of time in stop-and-go urban traffic, where its engine switches off frequently and it can move under electric power alone for short distances, or whether you do hundreds of miles a day on freeways, in which case a clean diesel is a better bet.

Designed to last a lifetime

Second, a hybrid’s high-voltage battery pack generally doesn’t need to be replaced over the lifetime of the car–or at least the first decade.

The nickel-metal-hydride (and now lithium-ion) battery packs in hybrids are very different to 12-Volt lead-acid starter batteries. They’re considered part of the vehicle’s pollution control system by regulators, so they must be warrantied for either 8 years//100,000 miles or 10 years/150,000 miles (depending on your state).

Beyond that, automakers know very well that replacing a pack (a Gen II Prius pack costs about $2,500) would be a huge customer dissatisfaction issue. The packs are built with plenty spare energy capacity, and they control them to operate within a very narrow state-of-charge range, usually between 40 and 60 percent.

The packs may not have 100 percent of their original energy capacity, but they still function as hybrids.

Battery chemistry is key

A technical note: The battery chemistries used by most manufacturers degrade only with duty cycles (usage) and NOT with time alone. Electric-car maker Tesla is one of the few exceptions: It uses consumer-grade lithium-ion cells, which lose energy capacity over time, even if you never use them.

So, while a hybrid car owner may theoretically need to replace the pack at some point, it most likely won’t be required until around the same time the car itself becomes uneconomical: 12 to 15 years or more.

As you point out, if your Saturn loses its engine, or even its transmission, there’s no sense in repairing it. The hybrid battery pack falls into that same group of components: the ones that usually last the life of the car, and whose failure determines when the car gets scrapped.

Toyota, incidentally, has said that the hybrid battery pack is one of its least-replaced items. The bulk of them are sold to repair accident damage, not because they failed.